The present invention relates to a device for automatically producing an opening or cavity in the side of a ceramic product during molding in a mould.
A technique for forming sanitaryware conventionally includes casting of the slip in chalk moulds, that is to say, moulds in which the absorbency of the chalk is used to dehydrate the ceramic slip during molding.
However, the molding methods according to said technique require lengthy periods for molding the items and even longer for drying the moulds.
Moreover, the life of the chalk moulds is relatively brief, since it is limited to around one hundred cycles.
Nowadays, said technique is increasingly substituted by molding with slip pressure casting in porous resin moulds.
Compared with molding using chalk moulds, this molding technique advantageously allows a significant reduction in cycle times and an important increase in the life of the moulds, which can be subjected to several tens of thousands of molding cycles.
The reduction in cycle times and, above all, the increase in the life of the mould justify the attempt to insert into it equipment which allows a set of operations which were conventionally performed manually to be carried out on the item produced, for example, the punching of overflow holes (washbasins, bidets, etc.) or water supply holes (flushing cistern).
When the axis of the holes is parallel with the mould release direction, these holes are easy to obtain (and often obtained) with fixed punches. In other cases, that is to say, when the axis of the holes is at an angle to the direction of mould release, to prevent the punch from damaging the item during mould release, the punch is removed before mould release.
For this punch removal operation there are known mechanical devices with various technological configurations which are housed in the mould, such as pneumatic cylinders, hydraulic cylinders or control cables.
However, the molding technique which uses these mechanical devices is not without problems.
A first problem relates to keeping the ceramic slip pressurized during item molding. The fluid slip, inserted in the mould by pressure casting, tends to easily fill the spaces between the mobile parts of the devices, required by the functional movements of the devices, meaning that the use of complex sealing systems which are not easily implemented is essential.
A second problem relates to the size of these devices inside the mould. Their arrangement in the moulds is often not compatible with the circuits which carry the fluids essential to implementation of the molding cycle through the mould and which allow correct mould operation.
This general difficulty with coexistence often means that the device cannot be made, due to the practical impossibility of physically positioning devices of this type in the moulds.
Further problems, linked to the previous ones, are: limited mould reliability over time; difficulty in inspecting the mould for any maintenance which may be required; difficulty in finding materials for making devices which combine satisfactory resistance to abrasion and to oxidation in contact with the slip.
These problems are added to by: difficulties in constructing the physical means which allow a movement of the punch suitable for its removal; and the high costs of such means.
The aim of the present invention is to solve all the problems in the prior art by providing a device for producing an opening or cavity in the side of a ceramic product during product molding in a mould, the mould having a molding cavity delimited by a molding surface with a window, the device comprising a punch joined on the window in such a way that it projects into or, vice versa, is retracted from the molding cavity. In the device according to the invention, the punch is deformable with variations in its rigidity. The device also comprises punch shape variation differential constriction means and actuator means for punch deformation which, in the active condition, are designed to change the shape of the punch by counteracting the opposite reaction of the constriction means. The constriction means and actuator means produce a controlled, anisotropic deformation of the punch designed to make the punch project into the molding cavity.